A passive optical network (PON) includes a passive optical power splitter/combiner that feeds individual branching fibers to end users. The PON also has a tree topology that maximizes coverage with minimum network splits, thus reducing optical power loss. In addition, a common fiber feeder part of a PON is shared by all optical network units (ONUs) WITH terminating branching fibers. Moreover, traffic sent downstream from an optical line terminal (OLT) at a local exchange is simply broadcast by an optical power splitter to every ONU. Sending traffic from an ONU upstream to a local exchange, however, requires accurate multiple access techniques in order to multiplex collision-free traffic generated by the ONUs onto the common feeder fiber.
At least four major categories of multiple access techniques for fiber have been developed. These techniques include: Time Division Multiple Access (TDMA), SubCarrier Multiple Access (SCMA), Wavelength Division Multiple Access (WDMA), and Optical Code Division Multiple Access (OCDMA).
In a WDM-PON network, each ONU uses a wavelength channel to send packets to an OLT at a local exchange. In addition, the wavelength channel constitutes an independent communication channel and may carry a different signal format from other wavelength channels carried by other ONUs connecting to the OLT.
Conventionally, a WDM-PON network is designed to make each hardware unit at each endpoint, as well as each wavelength selective multiplexing element in the network, tune to a unique wavelength. This design works for wavelength independent power splitting PONs. However, a network with such a design is difficult to manage and prone to errors. One of conventional ways to improve performance of such a design is to implement “colorless” end-point equipment. In a colorless WDM-PON network, an ONU has no intrinsic channel assignment. The ONU obtains a channel assignment by virtue of what fiber the ONU is attached to on the network. This typically assumes that the network uses a WDM device as a splitting element. The physical effects used in this type of network design are either injection locking of a broadband laser source, or reflective modulation of downstream light.
However, these conventional schemes for WDM-PONs are not ideal to provide a complete solution for prevention of errors. Furthermore, because a WDM device is required in such a network design and all PONs currently deployed use a wavelength independent power splitter, these schemes require PON reconstruction.
Therefore, there is a need to develop a WDM scheme that operates over a power splitting PON infrastructure that does not require wavelength selected ONUs.